Underground storage



1962 A. J. SHIVER 3,049,921

' UNDERGROUND STORAGE Filed Sept. 28, 1959 4 Sheets-Sheet l 3a 49 DPG 4s p+ INVENTOR. A.J. SHIVER BY ig a M F/ ATTORNEYS 1962 A. J. SHIVER 3,049,921

UNDERGROUND STORAGE Filed Sept. 28, 1959 4 Sheets-Sheet 2 42 4| 39 3| 32 34 fi P Q as 61 50 v 64 66 33 p s w' v 36 37 63 29 INVENTOR. A.J.SH|VER A TTORNEKS Aug. 21, 1962 A. J. SHIVER UNDERGROUND STORAGE 4 Sheets-Sheet 3 Filed Sept. 28, 1959 FIG. 3

INVENTOR. A J SHIVER A T TORNEVS Aug. 21, 1962 A. J. SHIVER 3,049,921

UNDERGROUND STORAGE Filed Sept. 28, 1959 4 Sheets-Sheet 4 4 32 92 A I A I 6 w 37 A A M Q INVENTOR. 4 A.J. SHIVER BY kdlgu E; M

A 7' TORNEYS United rates 3,049,921 UNDERGROUND STORAGE Amos J. Shiver, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Sept. 28, 1959, Ser. No. 843,010 17 Claims. (Cl. 73-302) This invention relates to the underground storage of fluids, such as gaseous ethylene, propane, butane, ammonia, etc., and liquids such as liquefied petroleum gas. In another aspect it relates to a method and apparatus for accurately locating the interface in an underground storage cavern or the like between two immiscible fluids having different densities, such as the interface formed between a pool of brine and a layer of liquefied petroleum gas (hereinafter termed LP-Gas) stored there-above in said cavern.

application is a continuation-in-part of my copeuding application Serial No. 745,109, filed June 27, 1958, now abandoned.

Constantly expanding production of fluids for the industries of this country and elsewhere has created a definite problem in providing suitable storage facilities for these fluids. In the petroleum industries, in particular, the problem of storage of gases such as ethylene, propane, butane, ammonia, etc., and liquids such as LP-Gas, is presently an urgent one due to the cost of storage in surface equipment, such as steel tanks, and due to the massive construction required to withstand the vapor pressure of such stored fluids. Also adding to this problem of adequate storage facilities is the fact that many industnies, particularly the LP-Gas industry, experience seasonal peak loads in the requirements of their products and corresponding seasonal slack periods. These fluctuations in requirements require large storage facilities and the advantages of storing such fluids in underground storage caverns have lately come to the attention of the industry.

These underground storage caverns are generally formed in impermeable earth formations either by conventional mining methods or, in some cases, by dissolving material with aqueous solvents or the like to create a storage space in soluble underground formations, for exarnple, in salt formations or domes. The resulting caverns are less expensive to provide than would be an equal volume of orthodox surface storage space and have proven their value in the storage of gases, such as ethylene, propane, butane, ammonia, etc., and liquids such as LP-Gas, and the like. After formation of the cavern, a pool of brine or other displacing liquid normally occupies the lower portion of the cavern and the product to be stored occupies the space in the upper portion of the cavern above the displacing fluid. Since the displacing fluid and stored product are generally immiscible and have different densities, an interface forms between these two fluids.

It is often necessary to know the location and keep track of the interface between the displacing fluid and the stored product in the cavern. For example, in order to determine the shape and size of a cavern, the amount of prodnot stored in the cavern, etc., it is necessary to first locate the interface. Moreover, it is often necessary to know the location of the interface so as to be able to maintain the level of iluids in the cavern, and to prevent stored product from passing up through the bottom of the wash pipe or eductor tubing which depends within the cavern. Because the cavern is located a substantial depth below the ground surface, the caverns access bore is relatively small, and the shape of the cavern is often irregular, many of the prior art methods of locating the interface level or depth have been found wanting.

Accordingly, an object of this invention is to accurately locate the interface in an underground storage cavern or the like between two immiscible fluids having different densities. Another object is to provide a method and apparatus for locating said interface in spite of the relative inaccessability of the cavern, the relatively small cavern access bore, and the irregular shape of the cavern. Another object is to provide apparatus which will indicate at the surface the location of said interface with accuracy and without requiring costly equipment. A further object is to provide a method and apparatus which will locate said interface in an easy, inexpensive manner and thereby make it possible to maintain accurate control over the level of fluids in the cavern. Other objects and advantages of this invention will become apparent from the following discussion, appended claims and drawing in which:

FIGURE 1 is a schematic elevational view in partial section of an underground storage cavern with associated means necessary to carry out the subject invent-ion;

FIGURE 2 is a view similar to FIGURE 1 illustrating a further embodiment of this invention; and

FIGURES 3 and 4 are views of other embodiments of this invention.

Referring now to the drawing, in which like parts have been designated with like reference numerals, and initially to that embodiment illustrated in FIGURE 1, a sealed, fluid-filled underground storage cavern generally designated 10 is shown. Cavern 10 is formed within a soluble underground formation 11, such as a salt formation. The practice of this invention is particularly applicable and accurate where the ratio of the cavern height to the total depth beneath the surface of the ground is less than /3.

This cavern 10 can be formed by the first drilling access bore or bore hole 12 from the surface of the ground through relatively insoluble overlying formations 13, such as surface soil, shale, limestone, sandstone, etc., and then into the top of the soluble formation 11. Following the drilling of the access bore 12, casing 14- is then inserted in the bore hole and set or secured therein by means of cement 16 so as to form a fluid-tight seal. Following the cementing of casing 14-, the bore hole is drilled at a reduced diameter to the ultimate location of the bottom of the subsequently formed cavern. Depending with in casing 14 in annularly spaced relation therewith is a tubing or eductor pipe 17', the length of which is known, the lower end of the pipe 17 being positioned near the bottom of the bore hole. Alternatively, another tubing (not shown) can be suspended within the cavern in concentric relation with tubing 17, this other tubing serving to protect the inner tubing 17 during the washing operation. The salt in formation 11 is then dissolved by circulating the solvent, such as fresh water, down through tubing 17, the resulting solution or brine formed by the action of the solvent on the salt formation being removed to the surface via the annulus 18 formed between casing 14 and tubing 17. It is advisable in many cases to occasionally reverse the circulation, that is, by pumping the solvent down through the annulus 18 and withdrawing the resultant solution from the progressively enlarged cavern upwardly to the surface via tubing 17. In many cases it is often desirable to protect the roof of the cavern and the casing foot, and control in some measure the shape of the cavern by introducing a protective blanket of hydrocarbon into the cavern and allowing it to float on top of the resulting pool of solution or brine 19. Suitable protective hydrocarbons include any of those which are immiscible with the wash solution and lighter than the wash solution, for example, LP-Gas or hydrocarbon material like that of the product subsequently stored in the cavern. The resulting cavern generally will have an irregular shape, such as that shown in the drawing, due to the fact that formation 11 may have some relatively insoluble materials embedded therein, such as anhydrite or gypsum, or may contain some relatively insoluble shale stringers, or its irregular shape may be due to variations in mining of washing operations. However, the cavern may have a regular shape, such as that of an upright or inverted cone, or can be somewhat cylindrical in shape.

A suitable method for forming underground storage caverns in a similar manner is that disclosed in US. 2,787,455, issued April 2, 1957, to R. S. Knappen.

After the cavern has been formed, product 21, such as propane, is then introduced in the cavern, for example, by pumping it down through annulus 18-, the resulting displaced wash solution 19 being removed from the cavern Via tubing 17, and an interface 22 being formed between product 21 and brine 19. When it is desired to remove product 21 from the cavern this can be done by introducing brine via tubing 17 and removing the thus displaced product via annulus 18.

As mentioned hereinbefore it is often necessary to locate the interface 22 formed between the wash solution or brine 19 and the stored product 21. According to the practice of one embodiment of this invention, the annulus 18 communicates at the upper end of casing 14 with a product conduit 26 having a valve 27 therein and op eratively connected to a product pump 28. A valved bypass line 29 is preferably operatively connected in conduit 26 so as to bypass pump 28. The upper end of tubing 17 is operatively connected to a brine or solution conduit 31which is similarly provided with a valve 32, and thereafter communicating with apump 33 and valved bypass line 34. The upper end of casing 14 is also in communication with a pressure sensing line 36 having a valve 37 therein, the other end of the pressure sensing line being operatively connected to a pressure diiferential gauge 38. The upper end of tubing 17 is also connected to a similar pressure sensing line 39 having a valve 41 therein, the other end of line 39 being similarly operatively connected to differential pressure gauge 38. Any type of difnulus 18 via conduits 44-, 52, and 31 into tubing 17, the interface within the tubing 17 being progressively moved toward the bottom thereof. During this operation the pressure gauge 38, which is still in communication with pressure sensing lines 36, 39, will indicate progressively increasing pressure. When the product in tubing 17 completely fills the same and there is no longer an interface within tubing 17, the pressure gauge 38 will indicate a substantially constant value above zero, indicating the complete filling of tubing 17 with product. At this time, pump 48 is stopped. The pressure differential is then used as an index of the product-brine interface, as will be detailed in a specific example hereinbelow, and after locating the interface the cavern is returned to norm-a1 operation. This can be accomplished by closing valves 47 and 53, as well as valves 37 and 41, and opening valves 46 and 51. As a result, product from tubing 17 is withdrawn via conduits 31, 43, 49, and 26, and is pumped by pump 48 back into the annulus 18. As a result, the interface within the tubing 17 will rise as the tubing 17 becomes filled with brine once again. The complete filling of tubing 17 with brine can be detected by any conventional means or, for example, by means of pressure gauge 42, the latter indicating a constant value when the tub ing 17 is completely filled with brine.

Where pressure gauge 50 is alternatively employed, the difference in the pressures read by gauges 42 and 50 will a be the same as those pressures read by differential pressure gauge 38 as described hereinbefore. That is, when the interface levels in the cavern and tubing are the same, gauges 42 and 50 Will read the same. When the tubing is filled with product and conditions stabilized, the differential pressure is determined by taking the difference beferential pressure gauge can be employed, such as a mera cury filled U-tube which functions as a manometer.

Alternatively, instead of providing pressure sensing lines 36, 39 and differential pressure gauge 38, the upper end of casing 14 can be provided with a conventional tween pressures indicated by gauges 42 and 50, pressure gauge 42 reading the higher pressure.

Referring now to the other embodiment illustrated in FIGURE 2, wherein parts similar to those of FIGURE l are designated with like reference numbers, cavern 10 is similarly formed in an underground formation 11, such pressure gauge 50. Preferably, the upper end or top of tubing 17 is operatively in communication with a conventional pressure gauge 42.

Direct communication between product line 26 and brine line 31 is had by reason of communicating conduits 43 and 44, these lines having valves 46, 47, respectively. The other end of conduit 44 is also in communication with the inlet of a small pump 48; Product line 26 is also in communication with another conduit 49 having a valve 51 therein. The other end of conduit 49 communicates with a conduit 52, one end of the latter communicating pressure, the opening of valves 46 and 47 permits the transfer of product from the cavern and annulus 18 to the tubing 17, via lines 26, 44, 43, and 31. As a result, annulus 18 and tubing 17 are now in communication and suflicient time is allowed to elapse so as to equalize temperature and pressure conditions within the tubing 17, annulus 18, and cavern 10, the interface in the cavern being at the same depth as the interface in the tubing 17.

After said elapse of time, valves 37 and 41 are opened (valves 46 and 47 remaining open and the other valves kept closed). As a result, differential pressure gauge 38 is placed in operation and since the pressures within tubing 17 and annulus 18 have been allowed to equalize,

as a salt formation. Depending within access bore 12 are casing 14 and tubing 17. In FIGURE 2, product line 26 is provided with a bypass line 29, having a valve 63 therein, this bypass line bypassing valve 27 in product line 26 as well as pump 28. Direct communication between product line 26 and brine line 31 is had by reason of line 64, having a valve 66 therein, the point of communication between lines 26 and 31 being intermediate valve 27 and pump 28. The direct communication b tween pressure sensing lines 36 and 39 is had by reason of a small line 61 having a valve 62 therein.

When it is desired to locate the interface 22, with tubing 17 normally filled with brine, valves 27, 66 and 62 are opened, while all other v-alvm remain closed. In this manner communication is had between annulus 18 and tubing 17 via lines 26, 64 and 31, and since the product in the cavern is at a sufiiciently high pressure, it will partially till the tubing 17 After a sufiicient lapse of time, such as to stabilize temperature and pressure conditions, the interface within tubing 17 will be the same depth as that interface in the cavern. After said elapse of time, valve 62 is closed and valves 37 and 41 are opened, thereby placing differential pressure gauge 38 in operation. Since the product within the annulus 18 and tubing 17 are at the same conditions of temperature and pressure, the pressure gauge 38 will read zero. Thereafter, valve 63 in product bypass line 29 is opened and valve 27 closed, and product is ptunped by means of pump 28 into the tubing 17 via conduit 64, with valve 66 therein also opened, and conduit 31. As the tubing 17 fills with product, the interface therewithin will progressively move to the bottom of the tubing and during this operation the differential pressure gauge 38 will indicate progressively increasing pressure. When the tubing 17 is completely filled with product, the pressure gauge 38 will indicate a substantially constant value above zero. The pressure dif ferential is then used, as in FIGURE 1, as an index of the product-brine interface level or location. When it is desired to return the cavern to normal conditions, valves 37, 41, 63, and 66 are closed, as is valve 62, and valves 27, 32 and valved bypass conduit 34 are opened, and product is pumped into the annulus 18 via conduit 26 by operating pump 28. As a result, the product in tubing 17 is displaced via conduit 31 and bypass conduit 34, the displaced product from the tubing being vented, burned, or returned to storage. As a result of this displacement, the interface gradually rises within the tubing 17. Complete filling of tubing 17 with brine can be indicated, for example, by the constant pressure indicated by pressure gauge 42.

As a specific example, applicable to FIGURES 1 or 2, assume that the length of the tubing or cavern eductor pipe 17 is known to be 1500 feet. After partially filling the tubing with product, such as propane, and stabilizing temperature and pressure condition so that the interface in the tubing is at the same level as that in the cavern, the average temperature of the cavern is estimated to be 130 -F. (This temperature being estimated from previous storage data.) After filling the tubing completely with product, the difierential pressure between the tubing 17 and annulus 18 is found to be p.s.i. As indicated hereinbefore, this pressure differential is used as an index of the product-brine interface level. The 10 p.s.i. pressure differential is the pressure due to the difference in hydrostatic head between the column of product in the tubing 17 and the column of product and brine in the annular space 18 and cavern. From the knowledge that the specific gravity of saturated brine at 130 F. is 1.178, and that of propane at 130 F. is 0.4394, we find that the pressure of saturated brine per foot of column is equal to (1.178)(62.424/144), or 0.51 p.s.i., and the pressure of propane per foot of column is equal to (0.4394) (62.424/144), or 0.19 psi. The length AB of that portion of the tubing immersed in 'brine below the interface level is found as follows:

(.51) (AB) =(.19) (AB) +10 (.32) (AB)=10 AB=31.2 feet By subtracting AB from the known length of the entire tubing, the product-brine interface in the cavern is located, i.e., 1500 minus 31.2 equals 1468.8 feet.

By allowing temperature and pressure conditions to stabilize before the interface determination, errors in the latter will be insignificant or minor even when using estimated cavern temperatures. For example, when the interface is 20 feet above the lower end of the tubing, a 10 F. error in estimating the cavern temperature will result in only 0.2 foot error in locating the interface level. This is greater accuracy than usually could be obtained by mechanical means, such as by locating the interface by means of an electric line interface detecting instrument.

Referring now to the embodiment shown in FIGURE 3, the access bore 12 communicating with fluid-filled cavern 10 is similarly provided with a casing 14 and an eductor pipe 17, with an annulus 18 formed therebetween. Product conduit 26 is connected to annulus 18 and brine conduit 31 connected to eductor pipe 17. A small tubing 71, such as a 1 pipe, depends within eductor pipe 17 with an annulus 72 formed therebetween, the lower end of tubing 71 terminating at a predetermined point within the cavern 10 above brine-product interface 22, preferably at a point adjacent the top or roof of the cavern.

The differential pressure gauge 38 is adapted to communicate with annulus 18 via pressure sensing line 36 and product conduit 26, and with the upper end of small tubing 71 via pressure sensing line 39.

Communication between annulus 18 and tubing 71 is accomplished via line 73 having valve 74 therein.

Brine conduit 31 can be provided with a sampling line 76 for the purpose of detecting the presence of product in eductor pipe 17.

The upper end of tubing 71 can be connected to a water line 77 for the purpose of admitting fresh water to dissolve any salt deposit which may build up within tubing 71 or eductor pipe 17. Line 77 can communicate with brine conduit 31 through branch line 78, having a valve 79 therein, for the purpose of withdrawing product from tubing 71.

In the operation of the embodiment shown in FIGURE 3, annulus 18 is normally filled with product and tubings 17 and 71 normally filled with brine. When it is desired to determine the location of the interface 22, valve 74 is opened, while all other valves remain closed; this permits product from the annulus 18 to flow via lines 26 and 73 into tubing 71, displacing brine therefrom through the lower end of tubing 71. When tubing 71 becomes filled with product, further introduction of product thereto causes such additional product to enter annulus 72, rising gradually to the top thereof. Evidence of the complete filling of tubing 71 with product, to point C, can be noted by opening sample line 76. When tubing 71 is completely filled with product, valve 74 is closed and after a sufficient lapse of time, such as to stabilize temperature and pressure conditions, valves 37 and 41 are opened, thereby placing differential pressure gauge 38 in operation. The differential pressure gauge reading is the difference in pressure due to the column of brine CA in eductor pipe 17 and the corresponding column of product CA in the cavern. The pressure differential is then used as an index of the product-brine interface level or location.

When it is desired to return the cavern to normal conditions, valves 79 and 32 can be opened, along with the valve in the bypass line 34, to permit the product in tubing 71 to escape under its own pressure to a remote and safe point of disposal.

As a specific example of the embodiment of FIGURE 3, assume that the lower end of small tubing 71 terminates at a known depth of 1900 feet. After filling the tubing 71 with the product, the differential pressure between it and annulus 18 is found to be 50 p.s.i. Assuming the cavern temperature is 110 F. and cavern pressure is 982 p.s.i., the specific gravity of propane at this temperature and pressure is 0.48 and the specific gravity of saturated brine is 1.19. The cavern pressure of 982 p.s.i. can be calculated for any given depth from the weight of the brine in annulus 72 or it can be measured by lowering a conventional pressure gauge to the required depth.

The length CA, between interface 22 and the lower end of tubing 71, is found as follows:

50 p.s.i.=(1.190.48)(CA)=(0.71)(CA) CA=50/0.71=70 feet By adding CA to the length of tubing 71, it is found that the interface is located at 1900 feet plus 70 feet, or 1970 feet below the well-head.

One of the advantages of the embodiment shown in FIGURE 3 is that the amount of product introduced into the tubing 71 is small and thus little time is required to reach equilibrium temperature and pressure conditions.

Referring now to the embodiment shown in FIGURE 4, depending within eductor pipe 17 is a telescopic pipe generally designated 81, with annulus 72 formed therebetween. Telescopic pipe 81 comprises a plurality of telescopic tubings 82, 83, 84; although three such tubings are shown, any number of such tubings can be used. The lowermost tubing 84 is suspended by cable 86 which passes upwardly through tubings 83 and 82, and through a stufling box 85 or the like in the upper end of tubing 82. Cable 86 passes over a pulley 87, then over depth measuring sheave 88, which is operatively connected to odometer 90, and is then wound on a storage or hoist means 89 which can be actuated by any suitable means.

The upper end of tubing 82 communicates with annulus 18 via tubing 91 having flow control valve 92 therein. Similarly difierential pressure gauge 355 communicates with tubing 82 via pressure sensing line 39 and with annulus 18 via pressure sensing line 35. The presence of product in eductor pipe 17 is again ascertainable by sampling line 76 in brine conduit 31,

In the operation of the embodiment shown in FIGURE 4, with telescopic tubing 81 depending within eductor pipe 17 such that the lower end of tubing 84 terminates at a point above interface 22, valve 92 is opened, while all other valves remain closed. Thus, product is permitted to flow from annulus 18 into tubing 81. The complete filling of tubing 81 with product will be indicated by the presence of some product in sampling line 76. When tubing 81 is filled with product, valve 92 is closed, either completely or partially, and valves 37 and 4 1 are opened, thereby placing differential pressure gauge 33 into operation. If the reading on gauge 38 indicates a reading greater than zero, this means that the lower end of tubing 84 is above interface 22, thus indicating that telescopic pipe 81 must be lowered further. This lowering is accomplished by lowering cable 86, which in turn lowers tubing 84, the length of the tubings 83, 84 being such that with incremental lowering it will be possible for the lower end of tubing 84 to reach a depth adjacent that of interface 22. After each incremental lowering, further product is introduced into tubing 81 to fill the same, and when gauge 38 reads Zero, the lower end of tubing 84 will be at interface 22. At this point in the operation, odometer 90 will give a direct depth reading of the interface 22.

If upon the first filling of telescopic tubing 81 with product, the gauge 38 reads zero this may also indicate that the lower end of tubing 84 is below the interface 22. In such a case, the telescopic tubing 81 can be raised a small distance, until the gauge gives a value greater than zero. By then lowering tubing 81, the interface 22 can be approached again and its true depth found.

Alternatively, a small pump can be placed in line 91 to pump product from the annulus '18 into tubing 81, and a differential pressure gauge employed which will read minus and plus differential pressures; this will permit the approach to the inter-face 22 from a depth below interface 22. In this case, the location of interface 22 will be indicated when the minus differential pressure reading changes to zero.

Instead of the telescopic tubing shown in the drawing, any other pipe arrangement which can be lowered into the cavern can be employed.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it is to be understood that the foregoing discussion and drawing illustrate preferred embodiments of this invention and do not unduly limit the same.

I claim:

1. In a sealed underground storage cavern comprising a'cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed there between, a method of locating said interface, which comprises suspending a tubing within said access bore in such a manner that the lower open end of said tubing communicates with said displacing liquid and is initially filled therewith, introducing a column of said fluid from said cavern into said tubing, the lower end of said column terminating at a predetermined point within said tubing, and measuring the pressure differential between said fluid of said column and said cavern, whereby said pressure differential can be used as an index of the location of said interface.

2. In'the process of storing a relatively lighter fluid over an immiscible heavier liquid in a cavern, in which a casing extends from the surface of the ground into said cavern and is filled with said fluid, and a tubing extends from the surface of the ground into and is filled with said liquid, the process of determining the elevation of the interface of said fluid and liquid which comprises the steps of extending a measuring tubing from the surface of the ground into said liquid to a predetermined known elevation spaced from said interface, forcing some of said fluid into said measuring tubing to completely displace said liquid therefrom, and measuring the differential pressure between the fluid in said casing and the fluid in said measuring tubing at the same elevation adjacent the surface of the ground to determine the elevation of said interfacetherefrom.

3. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity con taining in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed there- 'between, a method of locating said interface, which comprises suspending a tubing within said access bore and cavity in such a manner that the lower open end of said tubing is located at a point below said interface, allowing communication between the upper ends of said tubing and cavern so as to permit said fluid to be passed into said tubing and partially fill the latter therewith, allowing temperature and pressure conditions in said cavern and tubing to stabilize, introducing further said fluid into the upper end of said tubing so as to completely fill the same therewith, and measuring the pressure differential between said fluid in said tubing and said cavern, whereby said pressure differential can be used as an index of the location of said interface.

4. Ina sealed underground storage cavern comprising a cavity having a relatively large diameter defined by an impermeable formation, an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing brine in its lower portion and in its upper portion a stored fluid under pres sure and lighter than and immiscible with said brine with an interface formed therebetween, and a tubing of known length suspended within said access bore and defining therewith an annular space, said tubing having a lower open end located at a point below said interface and normally filled with brine, a method of locating the level of said interface, which comprises allowing communication between the upper ends of said tubing and annular space so as to permit the transfer of said fluid under its own pressure from said annular space into said tubing whereby the major portion of brine in said tubing is displaced, allowing temperature and pressure conditions in said cavern and tubing to stabilize, introducing further said fluid into the upper end of said tubing so as to completely fill the same therewith, and measuring the pressure differential between said fluid in said tubing and said cavern, whereby said pressure differential can be used as an index of the location of said interface.

5. In a sealed underground storage cavern comprising a cavity having a relatively large diameter defined by an impermeable formation, an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing brine in its lower portion and in its upper portion a stored fluid under pressure and lighter than and immiscible with said brine with an interface formed therebetween, and a tubing of known length suspended within said access bore and de fining therewith an annular space, said tubing having a lower open end located at a point below said interface and normally filled with brine, a method of locating the level of said interface, which comprises allowing com- 9 munication between the upper ends of said tubing and annular space so as to permit the transfer of said fluid under its own pressure from said annular space into said tubing whereby the major portion of brine in said tubing is displaced, allowing temperature and pressure conditions in said cavern and tubing to stabilize, Withdrawing said fluid from said annular space and pumping the same into the upper end of said tubing so as to completely fill the same therewith, and measuring the pressure differential between said fluid in said tubing and said annulus, whereby said pressure differential can be used as an index of the location of said interface.

6. The method according to claim further comprising displacing said fluid in said tubing by pumping further amounts of said fluid into the upper end of said annulus so as to fill said tubing with brine.

7. The method according to claim 5 wherein said impermeable formation is a salt formation, and said fluid is ethylene.

8. The method according to claim 5 wherein said impermeable formation is a salt formation, and said fluid is propane.

9. The method according to claim 5 wherein said impermeable formation is a salt formation, and said fluid is liquefied petroleum gases.

10. In a sealed underground storage cavern comprising a cavity having a relatively large diameter defined by an impermeable formation, an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing brine in its lower portion and in its upper portion a stored fluid under pressure and lighter than and immiscible with said brine with an interface formed therebetween, and a first tubing suspended within said access bore and defining therewith a first annular space, said first tubing having a lower open end located at a point below said interface and normally filled with brine, a method of locating the level of said interface, which comprises suspending a second tubing with n said first tubing, a second annular space being defined between said first and second tubings, said second tubing being of known length and terminated at a point adjacent the roof of said cavity, allowing communication between the upper ends of said first annular space and said second tubing so as to permit the transfer of said fluid from said first annular space to said second tubing, allowing temperature and pressure conditions in said cavern and said second tubing to stabilize, and measuring the pressure differential between said fluid in said first annular space and said second tubing whereby said pressure differential can be used as an idex of the location of said interface.

11. In a sealed underground storage cavern comprising a cavity having a relatively large diameter defined by an impermeable formation, an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing brine in its lower portion and in its upper portion in a stored fluid under pressure and lighter than and immiscible with said brine with an interface formed therebetween, and a first tubing suspended within said access bore and defining therewith a first annular space, said first tubing having a lower open end located at a point below said interface and normally filled with brine, a method of locating the level of said interface, which comprises suspending a second tubing within said first tubing, a second annular space being defined by said first and second tubings, allowing communication between the upper ends of said first annular space and said second tubing so as to permit the transfer of said fluid from said first annular space to said second tubing, allowing temperature and pressure conditions in said cavern and said second tubing to stabilize, measuring the pressure differential between said fluid in said first annular space and said second tubing, moving said second tubing a known distance within said first tubing and repeating the foregoing steps until said pressure differential is zero, whereby said pressure differential can be used as an index of the location of said interface.

12. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed there between, a tubing of known length suspended within said access bore and defining therewith an annular space which communicates with the upper portion of said cavity, said tubing having a lower open end located at a point below said interface, pressure measuring means operatively connected with the upper ends of said tubing and annular space, first and second conduit means operatively connected to said upper ends of said tubing and annular space, respectively, third conduit means operatively connected to and communicating with said first and second conduit means, valve means in each of said first, second and third conduit means, and pumping means operatively adapted to supply fluid from one of said first and second conduit means to other.

13. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed therebetween, a tubing of known length suspended within said access bore and defining therewith an annular space which communicates with the upper portion of said cavity, said tubing having a lower open end located at a point below said interface, a first pressure sensing conduit operatively connected at one end to the upper end of said annular space, a second pressure sensing conduit operatively connected at one end to the upper end of said tubing, a pressure differential gauge operatively connected to the other ends of said first and second pressure sensing conduits, first and second conduit means operatively connected to said upper ends of said tubing and annular space, respectively, third conduit means operatively connected to and communicating with said first and second conduit means, valve means in each of said first, second and third conduit means, and pumping means operatively adapted to supply fluid from one of said first and second conduit means to other.

14. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed therebetween, a tubing of known length suspended within said access bore and defining therewith an annular space which communicates with the upper portion of said cavity, said tubing having a lower open end located at a point below said interface, a first pressure sensing conduit operatively connected at one end to the upper end of said annular space, a second pressure sensing conduit operatively connected at one end to the upper end of said tubing, a pressure differential gauge operatively connected to the other ends of said first and second pressure sensing conduits, first and second conduit means operatively connected to said upper ends of said tubing and annular space, respectively, third conduit means operatively connected at one end with said second conduit means, pumping means the inlet of which is operatively connected to the other end of said third conduit means, fourth conduit means operatively connected at one end to said first conduit means and at the other end to the outlet of said pumping means,

fifth conduit means operatively connected at one end to said first conduit and operatively connected at the other end to said third conduit means at a first point, sixth conduit means operatively connected at one end to said second conduit means and at the other end to said fourth conduit means at a second point, valve means in each of said pre sure sensing conduits and said conduit means, said valve means in said third conduit means being located upstream from said first point, said valve means in said fourth conduit means being located downstream from said second point. i

15. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed therebetween, a first tubing of known length suspended within said access bore and defining therewith a first annular space which communicates with the upper portion of said cavity, said first tubing having a lower open end located at a point below said interface, a first pressure sensing conduit operatively connected at one end to the upper end of said annular space, a second pressure sensing conduit operatively connected at one end to the upper end of said tubing, a pressure diiferential gauge operatively connected to the other ends of said first and second pressure sensing conduits, a pressure equalizing conduit operatively communicating between said first and second pressure sensing conduits, first and second conduit means operatively connected to said upper ends of said tubing and annular space, respectively, third conduit means operatively connected to and communicating with said first and second conduit means, valve means in each of said first, second and third conduit means, and pumping means operatively adapted to supply fiuid from one of said first and second conduit means to other.

16. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said'displacing liquid with an interface formed therebetween, a first tubing suspended within said access bore and defining therewith a first annular space which communicates with the upper portion of said cavity, said first tubing having a lower open end located at a point below said interface, a second tubing of known length suspended within said first tubing, said second tubing terminating at a point adjacent the roof of said cavity and together with said first tubing defining a second annular space, a first pressure sensing conduit operatively connected at one end to the upper end of said first annular space, a second pressure sensing conduit operatively connected at one end to the upper end of said second tubing, a pressure differential gauge operatively connected to the other ends of said first and second pressure sensing conduits, first and second conduit means operatively connected to the upper ends of said first and second annular spaces, third conduit means operatively connected between the upper ends of said first annular space and said second tubing, valve means in each of said first, second and third conduit means and means to indicate the presence of fiuid in said second conduit means.

17. In a sealed underground storage cavern comprising a cavity having a relatively large diameter and an access bore having a relatively small diameter and extending from said cavity to the ground surface, said cavity containing in its lower portion a displacing liquid and in its upper portion a stored fluid lighter than and immiscible with said displacing liquid with an interface formed therebetween, a first tubing suspended within said access bore and defining therewith a first annular space which communicates with the upper portion of said cavity, said first tubing having a lower open end located at a point below said interface, a movable second tubing suspended within said first tubing and defining therebetween a second annular space, means to measure the length of said second tubing, means to lower and raise said second tubing, a first pressure sensing conduit operatively connected at one end to the upper end of said first annular space, a second pres sure sensing conduit operatively connected at one end to the upper end of said second tubing, a pressure differential gauge operatively connected to the other ends of said first and second pressure sensing conduits, first and second conduit means operatively connected to the upper ends of said first and second annular spaces, third conduit means o-peratively connected between the upper ends of said first annular space and said second tubing, valve means in each of said first, second and third conduit means, and means to indicate the presence of fluid in said second conduit means.

References Cited in the file of this patent UNITED STATES PATENTS 1,927,758 Scheel et a1 Sept. 19, 1933 2,360,742 Toth et al Oct. 17, 1944 2,972,708 Johnson et al May 21, 1957 FOREIGN PATENTS 159,674 Great Britain Mar. 10, 1921 

